The bone remodelling response to PTH, which is independent of vitamin D action, seems to be intact in these patients180, which suggests a possible increased risk of osteoporosis in patients with sustained increased levels of PTH despite treatment with calcium and vitamin D. Nevertheless, bone density seems to be normal to increased in patients with PHP1A, in particular in those who do not have excessive circulating levels of PTH218. The gene discussed is PTH; the disease is osteoporosis.